The present invention relates generally to pumps for viscous slurries, such as concrete, and more particularly to an apparatus and method for lining pipe with concrete using such a pump.
It is common to apply concrete or other corrosion-resistant linings to the interior surfaces of metal pipe. Small diameter pipe, up to sixteen inch diameter, for example, may be lined by depositing the lining material onto the interior surface of the pipe using a spray lance, and rotating the pipe to distribute the lining material about the interior surface and compact the lining material using centrifugal force. The spray lance may comprise a hollow tube having a spray nozzle at one end which is inserted into the pipe and advanced over the length of pipe as the lining material is pumped through the hollow tube to the spray nozzle and sprayed onto the surface of the pipe. As may be appreciated, it is desirable that the lining have a predetermined thickness and that the lining thickness be substantially constant over the length of the pipe. This requires the delivery of a predetermined quantity of lining material by the pump and reasonably close control over the pump so that the delivery of the lining material is accurately controlled and synchronized with the movement of the lance. Moreover, the pump must be a constant flow surgeless pump since any change in pump pressure and the flow rate from the pump would result in skips or thin spots in the lining.
Pumps which are capable of pumping viscous slurries such as concrete which have these and other desirable characteristics and features are difficult to find. Most known pumps for concrete mixtures and the like do not afford sufficiently accurate control over the starting and stopping of the flow to give linings having the desired characteristics. In addition, concrete mixtures are abrasive, and pump wear may result in a change in the flow rate from the pump, thereby necessitating close monitoring and control to insure that a predetermined flow rate is maintained. For pipe lining operations, it is desireable to be able to employ a concrete mixture having a relatively high sand-to-cement ratio. Most known types of concrete pumps have difficulty pumping mixtures having a high sand-to-cement ratio without the pump binding. It is also necessary that the pump be capable of easy cleaning since if the concrete mixture is allowed to harden within the pump, it could ruin the pump.
It is desirable to provide pumps for viscous slurries such as concrete and the like and to provide a method for pipe lining employing such a pump which avoid the foregoing and other disadvantages of known pumps and methods, and it is to these ends that the present invention is directed.